The present technology relates to secondary batteries including a cathode, an anode, and an electrolytic solution, electronic devices using the same, electric power tools using the same, electrical vehicles using the same, and electric power storage systems using the same.
In recent years, electronic devices represented by a mobile phone and a Personal Digital Assistant (PDA) have been widely used, and it has been strongly demanded to further reduce their size and weight and to achieve their long life. Accordingly, as a power source for the electronic devices, a battery, in particular, a small and light-weight secondary battery capable of providing a high energy density has been developed. In recent years, it has been considered to apply such a secondary battery not only to the foregoing electronic devices but also to various applications represented by an electric power tool such as an electrical drill, an electrical vehicle such as an electrical automobile, and an electric power storage system such as a home electrical power server.
As the secondary batteries, secondary batteries using various charge and discharge principles have been widely proposed. Specially, lithium ion secondary batteries using insertion and extraction of lithium ions are considered promising, since the lithium ion secondary batteries are able to provide a higher energy density than that of lead batteries, nickel cadmium batteries and the like.
The secondary batteries include a cathode, an anode, and an electrolytic solution. The cathode and the anode respectively contain a cathode active material and an anode active material that insert and extract lithium ions. In the secondary battery, in order to obtain a high battery capacity, a lithium-containing compound such as LiCoO2 is used as a cathode active material, and a carbon material such as graphite is used as an anode active material.
In the secondary battery using the carbon material as an anode active material, the anode active material is easily reacted with an electrolytic solution at the time of charge and discharge, and therefore decomposition reaction of the electrolytic solution tends to be promoted. In this case, since the surface of the anode is covered with a decomposed matter or the like of the electrolytic solution. Therefore, when charge and discharge are repeated, resistance of the anode is easily increased.
Therefore, it has been proposed to use, as an anode active material, a low reactive titanium-containing lithium composite oxide instead of the high reactive carbon material (for example, see Japanese Unexamined Patent Application Publication No. 06-275263). The titanium-containing lithium composite oxide is an oxide containing Li, Ti, and other metal element as an element, and has a spinel type crystal structure.